Study of proteins, phospholipids and cholesterol of rat bile during chronic drainage

Glycerophospholipids, cholesterol and proteins of rat bile were analyzed at different time-intervals during the bile duct cannulation over a period of 24 hr, to study a possible association between the secretion of these bile components. Glycerophospholipids and cholesterol decreased between the 16th-24th hrs, then rose again, showing a bile acid synthesis dependence. In contrast, during the entire collection period, protein concentration was normal. On gel electrophoresis bile proteins give a spectrum of fifteen discrete bands, three of them being Sudan black positive. Some, but not all bile protein bands, show a pattern similar to serum proteins both by means of SDS disc electrophoresis and of immunological techniques. According to the bile composition in GPL and cholesterol and the presence in bile of lipoproteins with SDS electrophoresis migration superimposable to apo-A-IV of serum high density lipoproteins, the following hypothesis is suggested to explain the origin and pathway that some fractions of bile can follow to reach biliary canalicula: some serum or membrane components (that is GPL, cholesterol and possibly apo-A-IV) might insert themselves into the outer leaflet of hepatocyte plasmamembranes at the sinusoidal side; from here they may slip over the inner plasmamembrane monolayer, through the junctions, to the canalicular region of the membrane to give rise, by the action of bile salts, to micelles of bile, together with components coming from other subcellular compartments, following different pathways.